FIG. 6 shows a conventional infrared microscopic spectrometer. Therein, infrared rays from a source 1 are incident upon a sample 3 through a condenser mirror system 2. The condenser mirror system 2 may be a Cassegrain object mirror system.
The light transmitted through the sample 3 is enlargedly focused into an image by a second object mirror system 4, which may also be a Cassegrain object mirror system. The image projected by the second object mirror system 4 is projected into a spectrometric system 5 and sent to a display device 6 for the purposes of carrying out an analysis.
It is not possible to obtain a transmission spectrum with the system depicted in FIG. 6 when a sample has an extremely strong absorption coefficient. For such high absorption samples, an attenuated total reflection (ATR) analysis must be conducted.
FIG. 7 shows a rough schematic depiction of an ATR analysis. Therein, incident infrared light is collected by collecting mirror system 7 and reflected from flat mirror 9 into an ATR crystal 11. The ATR crystal 11 is a reflecting, highly refractive optical medium. It is constructed of highly refractive materials such as KRS-5, germanium, or silicon. The ATR crystal is arranged within the optical path formed between flat mirrors 9 and 10, and a sample 12 is placed on one surface of the ATR crystal in contact with the crystal 11.
The infrared rays which are incident upon the ATR crystal 11 are totally reflected, and the infrared rays having a specified wavelength are absorbed by an ingredient to be measured within the sample 12. The wavelength absorbed depends upon the inducing radical of the ingredient to be measured within the sample.
The infrared rays passing through the sample 12, and being totally reflected by the ATR crystal 11, exit the crystal 11. The rays are incident upon the spectrometer (not shown) through the flat mirror 10 and the collecting mirror system 8 in order to obtain an infrared spectrum corresponding to the ingredient to be measured.
As shown in FIG. 6, the infrared microscopic spectrometer requires that the condenser mirror system 2 and the object mirror system 4 be arranged along a singular optical axis so that the infrared rays from the light source 1 travelling through the sample 3 may be used to provide an infrared spectrum. On the other hand, in an infrared spectrometer using the ATR method of analysis, the infrared rays exiting the ATR crystal travel along a different optical axis from the incident rays from the light source. Thus, an ATR analysis cannot be undertaken by an infrared microscopic spectrometer as shown in FIG. 6, and it is necessary to use a different measurement apparatus, depending upon the sample to be measured.
An infrared microscopic spectrometer which incorporates an apparatus for ATR analysis is shown in FIG. 8. Therein, flat mirrors 15, 16, 17, and 18 and collecting mirrors 13 and 14 are configured and reconfigured to provide a requisite optical path flowing through the ATR crystal 11 every time the incident angle of the infrared rays is altered or the sample is exchanged.